1. Field of the Invention
The present invention relates to a method of and apparatus for manufacturing a core wire for use with optical fibers.
2. Description of the Prior Art
Optical fibers for information transmission are now ready for practical use. A method of laying a plurality of stripes of optical fibers of this type over a long distance is disclosed in Japanese Patent Publication No. 60-37565. This method employs as a core wire a grooved filament composed of a wire of a diameter about 3 to 5 mm having one groove or a plurality of grooves provided in the outer periphery thereof longitudinally therealong. The wire is of a metal such as aluminium, iron and the like or alloys thereof or such plastics as fluorine plastics, etc., or such reinforced plastics as FRP. And, optical fibers are directly, or those coated with synthetic resin are, inserted into the groove or grooves, and the interior of the groove is preferably filled with silicon resin, etc., for holding the optical fibers therein. However, the core wire so structured was manufactured and employed up to now, for example, by merely extruding plastics. The core wire made of plastics has insufficient mechanical strength to resist stretching and bending. Accordingly, there is a need at present to provide a method and apparatus to mass-produce highly accurate core wires made of a metal material having sufficient mechanical strength both inexpensively and with satisfactory yield.
In addition, because there was no demand for the grooved metal strip described above until now, no prior art has been found now as a method of and an apparatus for manufacturing it. Japanese Laid-Open Patent Publication No. 59-39401, for example, discloses a rolling mill having a similar structure, although only in roll arrangement, to a rolling machine according to the present invention. This rolling mill is not adapted to manufacture the grooved strip described above, but merely to manufacture wire materials with circular cross sections. Likewise, Japanese Laid-Open Patent Publication No. 59-39401 discloses a rolling mill for manufacturing a steel bar. This, however, is not adapted to manufacture a grooved wire, too. Another example of the prior art to manufacture the grooved wire of the type above is found in Japanese Patent Publication No. 60-37565, which provides a composite optical fiber overhead line having an optical fiber unit produced by inserting an optical fiber core wire into a groove provided in the outer periphery of a grooved strip and filling the groove with silicone resin.